High Resolution Projection Micro-Stereolithography System And Method

ABSTRACT

A high-resolution PμSL system and method incorporating one or more of the following features with a standard PμSL system using a SLM projected digital image to form components in a stereolithographic bath: a far-field superlens for producing sub-diffraction-limited features, multiple spatial light modulators (SLM) to generate spatially-controlled three-dimensional interference holograms with nanoscale features, and the integration of microfluidic components into the resin bath of a PμSL system to fabricate microstructures of different materials.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a divisional of prior application Ser. No.13/149,773, filed May 31, 2011, which claims the benefit of U.S.Provisional Application No. 61/349,627, filed May 28, 2010, all of whichis incorporated by reference herein.

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The United States Government has rights in this invention pursuant toContract No. DE-AC52-07NA27344 between the United States Department ofEnergy and Lawrence Livermore National Security, LLC for the operationof Lawrence Livermore National Laboratory.

FIELD OF THE INVENTION

The present invention relates to projection micro-stereolithography(PμSL) systems and methods, and more particularly to an improvedhigh-resolution PμSL system and method having one or more of thefollowing features; a far-field superlens for producingsub-diffraction-limited features, multiple spatial light modulators(SLM) to generate spatially-controlled three-dimensional interferenceholograms with nanoscale features, and the integration of microfluidiccomponents into the resin bath of a PμSL system to fabricatemicrostructures of different materials.

BACKGROUND OF THE INVENTION

Stereolithography (SL) is a known rapid prototyping technology whichenables the generation of scale models of complicated three-dimensionalparts in a fraction of the time and at a fraction of the cost oftraditional methods. Generally, SL involves the use of electromagneticradiation (e.g. a UV laser beam) to cure a photosensitive liquid (e.g.liquid photosensitive monomer or resin) which solidifies upon exposureto electromagnetic radiation of a given wavelength. When a layer isfully solidified upon exposure, the component stage drops down to allowa fresh layer of photosensitive liquid to flow over the solid surface.In this manner, a three-dimensional (3D) structure is fabricated fromthe bottom up, a layer at a time. SL provides a useful tool forvisualizing components to assist in the iterative design process, aswell for the direct fabrication of functional parts and microdevices.

Various stereolithographic methods are known for three-dimensionalfabrication of microsystems. A first basic technique uses a scanninglaser system to serially trace the shape of the desired part in aline-by-line manner over the free surface of a photosensitive resinbath. The laser is controlled by a CAD system that functions as anelectronic mask, and typically allows for a transverse resolution ofabout 150 μm. In addition, the photopolymer can be loaded with ceramic,metal, or other particles to generate components of different materials.After initial stereolithographic fabrication, the parts can be sinteredto remove the polymer and densify the functional material of interest.This usually shrinks the part by some controllable amount. Animprovement on the scanning laser technique is known as the “Two PhotonAbsorption” method. This process uses two low power, pulsed laser beamswhich intersect deep within the resin bath. At the intersection point,the beams form a small volume which has sufficient photon flux topolymerize only the local material in the volume. While the beams canwrite a completely three-dimensional pattern into the resin bath, thisis typically a slow process because it writes in a point-by-pointfashion. Moreover, the types of resins available for this technique areseverely limited due to the need that they be highly transparent to thelaser beams, which also effectively prevents the loading of ceramic ormetal particles in the resin bath.

Projection micro-stereolithography (PμSL) is a third, low cost, highthroughput, micro-scale, stereolithography technique which projects atwo dimensional image onto a photosensitive resin bath rather than asingle spot, to fabricate complex three-dimensional microstructures in abottom-up, layer-by-layer fashion. Originally, PμSL was firstaccomplished by using a set of photomasks to project the two-dimensionalimage. Although effective, this method requires a large number ofphotomasks thus limiting the practical number of layers possible. Theuse of a dynamically reconfigurable mask, via a spatial light modulator(SLM) in PμSL systems dramatically reduced process time resulting instructures with thousand of layers. This was demonstrated in the form ofa liquid crystal display (LCD) in the paper “Ceramic Microcomponents byMicrostereolithography” by Bertsch et al (2004 IEEE). However, the LCDhad some intrinsic drawbacks including large pixel sizes and lowswitching speeds.

The use of a Digital Micromirror Device (DMD, a trademark of TexasInstruments) as the SLM in a PμSL system is described in the paper“Projection Micro-Stereolithography Using Digital Micro-Mirror DynamicMask” by C. Sun et al (2005 Elsevier). Similar to conventional SLtechniques, PμSL with a SLM is capable of fabricating complexthree-dimensional microstructures in a bottom-up, layer-by-layerfashion. A CAD model is first sliced into a series of closely spacedhorizontal planes. These two-dimensional slices are digitized in theform of an electronic image and transmitted to the SLM. A UV lamp or LEDilluminates the SLM which acts as a dynamically reconfigurable photomaskand transmits the image through a reduction lens into a bath ofphotosensitive resin. The resin that is exposed to the UV light is curedand anchored to a platform and z-axis motion stage. The stage is thenlowered a small increment and the next two-dimensional slice isprojected into the resin and cured on top of the previously exposedstructure. This layer-by-layer fabrication continues until thethree-dimensional part is complete.

It is also known that imaging and lithography using conventional opticalcomponents is restricted by the diffraction limit. Features resolutionin these systems is

limited to one half of the wavelength of the incident light because theycan only transmit the propagating components emanating from the source.It would be advantageous to provide an improved PμSL-based fabricationsystem and method capable of fabricating three-dimensional structureshaving sub-diffraction limited features, as well as other capabilitieswhich enhance the resolution, materials flexibility, and processperformance of standard PμSL.

SUMMARY OF THE INVENTION

One aspect of the present invention includes a projectionmicro-stereolithography (PμL) system for producingsub-diffraction-limited features, comprising: a light source; a spatiallight modulator (SLM) illuminated by the light source; a reduction lens;a stereolithographic bath containing a photosensitive resin; and afar-field superlens (FSL) contactedly interfacing the photosensitiveresin, said FSL including a dielectric layer and a metal grating layer,wherein the FSL is arranged to convert a far-field image produced by theSLM and reduced by the reduction lens into a near-field image for curingselect regions of the photosensitive resin.

Another aspect of the present invention includes a projectionmicro-stereolithography (PμSL) system, comprising: a light source; aspatial light modulator (SLM) illuminated by the light source; areduction lens; a stereolithographic bath containing a photosensitiveresin; and a microfluidic system integrated with the stereolithographicbath, said microfluidic system having at least one inlet portfluidically connected to deliver at least one type of photosensitiveresin from at least one source, and at least one outlet port.

Another aspect of the present invention includes a holographicprojection micro-stereolithography (PμSL) system, comprising: astereolithographic bath containing a photosensitive resin; and at leasttwo light projection systems, each projection system comprising a lightsource; and a spatial light modulator (SLM) illuminated by the lightsource for illuminating the photosensitive resin with a digital image,so that the holographic interference of all the digital images in thephotosensitive resin cures select regions of the photosensitive resin.

Another aspect of the present invention includes a holographicprojection micro-stereolithography (PμSL) system, comprising: a bathcontaining a photosensitive resin; and at least two light projectionsystems, each projection system comprising a light source; and a spatiallight modulator (SLM) adapted to produce a digital image whenilluminated by the light source, wherein the at least two lightprojection systems are arranged to holographically interfere saiddigital images in the photosensitive resin, to cure select regionsthereof.

And another aspect of the present invention includes aholographically-controlled volumetric curing method of photosensitiveresin, comprising: providing a bath containing a photosensitive resin,and at least two light projection systems, each light projection systemcomprising a light source and a spatial light modulator (SLM) adapted toproduce a corresponding digital image when illuminated by the lightsource; activating the light projection systems to produce the digitalimages; and directing the digital images of the light projection systemsto holographically interfere in the photosensitive resin so as tovolumetrically cure select regions thereof in a holographic interferencepattern.

Generally, the present invention involves an improved high-resolutionPμSL system and method capable of rapidly fabricating complexthree-dimensional meso- to micro-scale structures and components withmicro/nano-scale precision (i.e. including sub-diffraction-limitedfeatures). Similar to conventional PμSL, the present invention utilizesa SLM (such as for example a DMD or a Liquid Crystal on Silicon (LCoS))as a dynamically reconfigurable photomask to project a two-dimensionalimage onto the tree surface of a photosensitive resin bath. The resin iscured and lowered a small increment into the bath and a new image isprojected and cured on the top of the previously developed structure, tobuild a three-dimensional part in a layer-by-layer fashion, from thebottom up. Additionally, the PμSL system and method of the presentinvention also incorporates one or more of the following functionalfeatures to improve resolution, flexibility, and process performance ofstandard PμSL; an integrated far-field superlens (FSL) which overcomesthe diffraction limit of light (i.e. one-quarter wavelength) to producenanometer scale features (tens of nanometers or less than one-quarterthe UV light wavelength) on a wide range of substrates; and multipleSLMs arranged to generate spatially-controlled three-dimensionalinterference holograms with nanoscale features in a photosensitive resinbath of the PμSL to fabricate three-dimensional structures with a singleexposure; and microfluidic components integrated with the photosensitiveresin bath in order to use laminar flow control to optimally deliver anddistribute multiple photosensitive resins and other materials, so as toproduce multi-material microstructures.

Far-Field Superlens (FSL)

The FSL used in the present invention is a thin-film grating-typestructure (e.g. thin-film silver grating) which amplify evanescent waves(which decay exponentially in mediums with positive permittivity andpermeability and carry subwavelength information) to produce featureswhich exist below the diffraction limit. In particular, as used in thepresent invention, the thin-film grating-type structures of the FSLconvert amplified evanescent waves into a propagating field, and thusconvert a near-field effect into a far-field phenomenon. It is notabletherefore that the fabricated sub-wavelength features are not simply areduced or smaller version of the projected image from the SLM. There isnot a 1:1 pattern transfer. Because the SLM projected image is passingthrough a grating, sub-wavelength features on the other side of thegrating are fundamentally different in geometry to that which wasprojected. Therefore the SLM projected far-field image is calculated togenerate the desired sub-wavelength features on the other side of theFSL grating.

The FLS takes the form of a thin layer of material with either negativepermittivity or permeability (resulting in a negative index ofrefraction). Noble metals such as silver are good candidate materialsfor the FLS due to the ability to generate negative permittivity by thecollective excitation of conduction electrons. The thin metal gratinglayer is designed such that, the surface plasmons match the evanescentwaves being imaged so that the FLS enhances the amplitude of the field.Features as small as 5 μm for example have been demonstrated.

The FSL includes a metallic grating layer connected to a dielectriclayer. The dielectric layer is selected from a material that istransparent to the wavelength of a given light source, and has adielectric permittivity that matches that of the metal layer (which mayalso be a metal-based composite or multilayer). Example types includeglass, quartz, PMMA, PDMS, parylene, mineral oil, other oils, GaAs, ITO,etc. The thickness of the dielectric layer will be dependent on strengthof evanescent wave, and in particular, should be less than the projecteddistance of the evanescent wave which is at most hundreds of nanometers.Dielectric layer thickness may be chosen based on the metallic gratinglayer thickness because different metal-wavelength combinations willhave stronger Plasmon resonances and thus stronger projected evanescentwave fields. It is notable however, that this is typically within somesmall band, and still have to be very thin.

For the metallic grating layer of the FSL, a grating pattern isnecessary for converting far-field images to near-field, though it canbe dynamical, i.e. it can be generated optically, electrically oracoustically. It is appreciated that a non-grating thin metal film willform a simple near-field superlens. The periodicity of the gratingpattern may be designed based on the wavelength of the light source anddesired feature resolution. For example, a silver grating FSL for PμSLintegration has been constructed having a periodicity of about 200 nm, asilver line width of 100 nm and a thickness of 50 nm. The grating aspectratio (length/width) can be increased to produce a larger FSL and morearea over which to fabricate. The metal grating layer thickness may befrom tens of nanometers to hundreds of nanometers. Example types ofmetals may include, for example, silver, which is suitable for longer UVwavelengths (300-400 nm), or other metals such as for example aluminum,copper, gold, conductive oxides (ITO, doped ZnO), Na, K, Au—Ag alloy,Co—Au, Ni—Ag alloy, multi-layered graphenes, etc.

It is appreciated that the metallic grating layer may also be formed asa multilayer comprising several thin film layers of other materials,such as for example the combination of silver/MgO/silver composite (orsilver, Al₂O₃, silver) which could serve as a superlens for wavelengthof 500 nm. Such metal composite/multilayers may enable operation of theFSL at other wavelengths or simply may provide an alternative to silverin the UV range. The layers of the multilayer can consist of a seed oradhesion layer such as germanium or MgO. This is intended to providesmooth growth of metallic layer such as Ag or Au. There is also acomposite layer made of metal and dielectrics, such as MgO/Ag/MgO/Ag . .. thin film stacks, or it can contain porous anodized Al2O3 or TiO2 withelectroplated metal, such as Ag, Au, or conductive oxide fillers. Theimportance of the composite layer is to provide a impedance matchingelement for resonant transfer of evanescent waves. In addition, a layeris integrated to convert evanescent waves to far field. This can beimplemented such as metallic grating or dynamic grating produced byphotorefractive effect or electro-optical effects.

It is appreciated also that the FSL could be electro-optically tuned andpotentially integrated with UV-emitters. For example, a ZnO nanowireemitter may be integrated with the FSL such that each of the emitterscould be individually actuated, with tightly confined light spot withvirtually no crosstalk. They may be used in combination with digitalprojection from far field, for near field pattern generations.

Digital Holographic PμSL

Digital holographic masks are also used in the present invention, whichallows a variety of porous structures and materials to be establishedand aperiodic features to be intentionally positioned. In particulardigital dynamic masks are used to project the computed hologram intoliquid polymers for fabrication of highly interconnected functionallygraded density materials with nanometer precision. While holographicnanolithography is a known method of 3D volumetric nanofabrication byinterfering multiple coherent beams interfere in 3D space, the simpleinterference method typically cannot create designed defects andfeatures of arbitrary shape. They are typically also limited by thedepth of penetration in the solid photoreactive materials.

The present invention utilizes multiple light projection systems toproject respective digital images to the fabrication zone, so as toholographically interfere and thereby cure select portions of thephotosensitive resin, which is preferably chosen for photo-sensitivityand transparency. While the resin bath may be loaded with metal orceramic powders, this will change the optical properties. Methods suchas atomic layer deposition and electroplating may be used to infiltratethe polymer mold with liquid phase chemical reactants at lowtemperature.

Integration of Microfluidic Systems for Multi-Material Fabrication

Another feature of the present invention is the integration ofmicrofluidic components and sub-systems (in particular laminar flowsystems) with the PμSL system to provide the capability of fabricatingstructures (such as 3D structures) with multiple, heterogeneousmaterials in the same component. By incorporating microfluidic systemsinto the resin bath of a PμSL system, the present invention has theability to fabricate microstructures of different materials in oneprocess. By slowly flowing layers of photosensitive resin a singleexposure and curing step in one material can be completed. A newmaterial (different resin or loading of metal/ceramic particles) canfollow in another fluid layer. This material can then be exposed andcured resulting in a multilayer material. If the fluid is allowed tosettle in void areas then multiple materials can be cured on the sameimage plane and concentric structures of different materials (such asdouble shelled targets) may be fabricated. Laminar flow microfluidicsystems in particular provide for more uniform delivery and distributionof materials and to allow for multiple material components to besequentially exposed.

Various types of materials (various photosensitive liquids or slurrieswith metal or ceramic nanoparticles) may be injected into thefabrication area through a single, valved, microfluidic channel and portallows for the ability to sequentially fabricate with differentmaterials. For example, one material can flow into the fabrication zoneand layers lithographically formed. This material then is removed viaanother microfluidic port while a new material flows into thefabrication zone. More features/layers may then be produced. Themultiple materials could be in the same device layer or could form alayered structure. Furthermore, micofluidic integration may beimplemented with multiple injection ports for various materials. Theseports could be arranged around the fabrication area in almost anydesired geometry including radially oriented or at different verticalpositions. This would allow for more precise injection of differentmaterials to specific locations in the fabrication zone. The injectioncould occur simultaneously or could be staged in time depending on thepart to be fabricated. In general, this will allow for additionalmaterial and geometric flexibility in final fabricated part.

The introduction of different types of materials in to the bath vesselmay be enhanced by enclosing the fabrication zone and liquid with amembrane cover. The membrane can be made of PDMS or any other relativelyinert material; however it needs to have some gas permeability and beoptically transparent. The membrane provides several advantages; 1) itdampens any disturbances on the free surface of the liquid monomer bath(this increase fabrication speeds) and 2) it creates a completelyenclosed fluidic bath which results in smooth fluid flow aroundfabricated features. The membrane must be permeable so that there is athin layer of gas between the membrane and the liquid otherwisefabricated features may stick to the membrane. The below figures showand schematic of how the membrane can be integrated into the PμSL systemand some multimaterial parts fabricated with this technique.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated into and form a partof the disclosure, are as follows.

FIG. 1 is a flow diagram schematically illustrating the optical pathtaken in a first exemplary embodiment of the present invention forproducing sub-diffraction-limited features.

FIG. 2 shows a schematic view of a second exemplary embodiment of thepresent invention incorporating a far-field superlens in the opticalpath of the PμSL to produce sub-diffraction-limited features of 3Dmicro- and nano-structures in a layer-by-layer stereo lithographicfabrication process.

FIGS. 3A-C show schematic views of three exemplary methods ofsuperlens-liquid interfacing.

FIG. 4 shows a schematic view of another exemplary embodiment of thepresent invention showing multiple projection systems producing astructure based on a digital hologram generated by multiple SLMsarranged around a photosensitive resin bath for patterning 3Dnanostructures without periodicity.

FIG. 5 shows an isometric illustration of three dynamically configurablemasks corresponding to three interfering beams which produce a hologramof a complex 3D structure in a photosensitive resin bath to fabricatethe 3D structure in a single snapshot/exposure.

FIG. 6 shows a schematic view of an exemplary microfluidic system of thepresent invention for injecting multiple types of photosensitive resinsinto a hath vessel of a PμSL system.

FIG. 7 is a top view of an exemplary bath vessel of a PμSL having threeinjection ports and three outlet ports of an integrated microfluidicsystem.

FIG. 8 is a schematic view of another exemplary embodiment of the systemof the present invention incorporating multiple SLMS for 3D holographicstereolithography and a microfluidic system for using multiplematerials.

DETAILED DESCRIPTION

Turning now to the drawings, FIG. 1 shows a flow diagram generallyillustrating the primary components and the optical path of a firstexemplary embodiment of a PμSL system 10 of the present invention toproduce three-dimensional structures (e.g. meso- or micro-scale) withsub-diffraction-limited features. As shown in FIG. 1, the system 10generally includes a light source 11, such as for example a UV LEDarray, which produces electromagnetic radiation (hereinafter “light”) ofa given wavelength, (e.g. 350 nm for UV). The system also includes a SLM12 which functions as a dynamically configurable mask to produce atwo-dimensional pattern/image from the light. The two dimensional imageproduced from the SLM 12 is then reduced by a reduction lens 13, andprojected onto an FSL 14 which is positioned adjacent a photosensitiveresin bath 14. The reduced two dimensional image from the SLM (i.e. farfield image), is converted by the FSL 14 into a differenttwo-dimensional image (i.e. near-field image) havingsub-diffraction-limited features, i.e. features which exist below thediffraction limit. The near-field image then selectively cures localregions within the resin bath 14.

It is appreciated that the photosensitive resin bath contains a liquid,such as a liquid photosensitive monomer or resin, which is formed into acomponent when illuminated with the projected beam. In particular, theliquid converts to solid upon exposure to output of the superlens.Example material types include hexandiol diacrylate (HDDA), polyethyleneglycol diacrylate (PEGDA), tBA-PEGDMA (a shape memory polymer),POSS-diacrylate, and there could also be nanoparticles in the liquidsuch as gold, copper, or ceramics. The photosensitive resin may also beloaded with ceramic, metal, or other particles to generate components ofdifferent materials. In this case, after initial stereolithographicfabrication, the parts can be sintered to remove the polymer and densitythe functional material of interest. This usually shrinks the part bysome controllable amount. It is also notable that by varying theintensity of the UV light, various porosity/density structures can begenerated resulting in graded density materials. This could be combinedwith the superlens or holographic projection to generate graded densitystructures with <100 nm features.

FIG. 2 shows a second exemplary embodiment of the PuML system of thepresent invention having a light source 26 (shown as a UV source) whichilluminates a SLM 28 via a beam splitter 27, and a reduction lens 25which projects the image onto a FSL 30. The SLM is shown connected to acomputer 29 which dynamically controls the SLM to produce variousdigital masks, such as masks i, j, and k. It is appreciated that thetwo-dimensional image formed by the SLM are not the actual part orfeatures, rather they are the far-field image calculations correspondingto the desired near-field images to be produced by the FSL 30 which arethen used to selectively cure portions of the photosensitive resin, aspreviously described in the Summary. As shown in FIG. 2, the FSL ispositioned to contactedly interface directly with the photosensitiveresin at a liquid surface 22. The resin is shown contained in astereolithographic bath vessel 21, which is open at the top. A z-axisstage 23 and 24 is also provided for lowering the part (such as 31) aseach layer is fabricated. The z-axis stage 23, 24 is also shownconnected to the computer 29 so as to be controlled by the computer aseach level is completed.

FIGS. 3A-C show three different embodiments by which the FSL mayinterface with the photosensitive liquid resin. Although the FSL ischaracterized as “far-field”, this is only referring to one side of thelens. When a SLM-produced two-dimensional image is projected onto theFSL from the far-field, the FSL then generates near-field sub-wavelengthfeatures in the liquid monomer resin bath. Also, in order to have therequired surface plasmons for the lens to work, the thin film of silvermust have an interface with a dielectric material. It is appreciatedthat the FSL itself must be maintained in close proximity to thephotosensitive liquid. However, it may not be desirable to use theliquid resin/monomer as the dielectric material since the fabricatedfeatures may simply stick to the FSL. FIG. 3A in particular shows an FSL42 having a dielectric layer 43 and a metal grating layer 44 interfacedwith the photosensitive resin 40 at a liquid surface 41. In particular,the metal grating layer 44 is shown without an intermediate dielectricmaterial separating it from the resin, and instead directly contacts thephotosensitive resin. And incoming light (e.g. the projected image) isshown at 45. FIG. 3B shows a second embodiment of the FSL 46 also havinga dielectric layer 49 like FIG. 3A, but now also having an intermediatesolid dielectric layer 48 which is formed (e.g. coated) over themetallic grating layer 47. The coating may be a very thin layer, e.g.<100 nm to provide the metal dielectric interface. Example materialtypes may include PMMA, PDMS, glass, etc. And in FIG. 3C, anotherembodiment is shown having a dielectric layer 51, and where anotherliquid 52 (such as an oil) is used as the dielectric interlayer. Asshown in the figure, a thin layer of the liquid dielectric 52 willremain in contact with the FSL 50 due to surface tension effect. Similarto the solid dielectric, the liquid dielectric interlayer provides themetal dielectric interface. In this case, the liquid 52 fills voids inthe grading via surface tension effects and can provide a very thinlayer, it also prevents cored components from sticking to the FSL.Example material types may include mineral oil, and other oils. The FSLmay be held in placed on top of the liquid surface by conventionalmounting hardware known in the art or, for example, on a motion stage toensure good positioning. Furthermore, the FSL may be placed to cover thefree liquid surface (in whole or in part).

FIG. 4 shows a second exemplary embodiment of the system 80 of thepresent invention, with multiple electromagnetic radiation projectionsystems 81-83 together stereolithographically producing athree-dimensional structure 85 based on a digital hologram generated bythe multiple projection systems. The structures may be aperiodicstructures, designed features, or even fully 3D holograms. Inparticular, the projection systems 81-83 each have integrated SLMs (notshown) to produce digital masks, and are arranged around aphotosensitive resin hath vessel 83 to produce a 3D holographicinterference pattern in liquid resin for patterning 3D nanostructureswithout periodicity. The vessel 83 is shown as with opticallytransparent walls so that projections systems 82 and 83 may illuminatefrom the sides. The projection system 81 illuminates from the topthrough the open top side of the vessel 83 where the liquid level 84 isshown. A stage 86 (such as a z-axis stage) may also be provided wherethe holographically produced structure may be positioned.

Similarly, FIG. 5 shows an isometric illustration of three dynamicallyconfigurable masks 91-93 corresponding to three interfering beams whichproduce a hologram of a complex 3D structure 90 in a photosensitiveresin bath to fabricate the 3D

structure in a single snapshot/exposure. The three masks are shownorthogonally oriented, such as on xyz-axes. However, as shown in FIG. 8,multiple projection systems need not be orthogonal to each other. It isappreciated that each of the projections systems may also incorporate aFSL to produce sub-diffraction limited features when holographicallyinterfered with the near-field images from the other projection systems.The holographic lithography interferes light beams from multiple digitalmasks rather than lasers, and can provide individual pixel control. Withthis control, the interference pattern between the two or more beams canbe changed in 3D space resulting in locally controlled features andaperiodic structures. In addition, true 3D holograms may be generatedand projected into the photosensitive monomer to generate 3D structures(without the need for Z-stage adjustment).

FIG. 6 shows another exemplary embodiment of a microfluidic system 100of the present invention, integrated with a larger PμSL system (notshown) to enable materials flexibility, i.e. fabricating multi-materialscomponents, with multiple materials in either the same layer or acrosslayers. This allows a broad range of materials to be used with PμSL toinclude metals, ceramics and a range of polymers. FIG. 6 shows inparticular a PμSL bath vessel 101 having a cylinder 102 and a piston103. The top of the cylinder is open and contains a photosensitiveresin. The top of the piston 103 is shown as the fabrication stage andis connected to a z-stage 104 for lowering/elevating the fabricatedpart, typically in a layer-by-layer process. The cylinder 102 walls maybe optically transparent so as to enable illumination by imageprojectors (not shown). The system 100 is shown having an inlet 108fluidically connected to at least two different photosensitive resinsources 106 to 107, which are connected to supply the vessel withdifferent photosensitive liquids. A control valve 109 is shown connectedto a computer 105 (or other controller) for controlling injection ofresin into the bath vessel. An outlet port 110 is also shown forexhausting photosensitive liquid from the hath container, so that thevessel may be emptied of a first photosensitive liquid used to produce afirst feature of a fabricated structure prior to tilling with a secondphotosensitive liquid used to produce a second feature of the fabricatedstructure. And a control valve 111 is also shown connected to thecomputer 105 for controlling flow out of the vessel.

FIG. 6 also shown a membrane 112 which may be positioned at the liquidsurface, so as to enable laminar flow when resin is moved in and out ofthe vessel. The membrane is preferably optically transparent, as well asflexible so as to deform when fluid is moving in/out and eliminateliquid free surface disturbance. Optionally, the membrane may be gaspermeable. Example material types include PDMS, glass, quartz, and otherclear flexible polymers. It is notable that if an FSL is used, themembrane may or may not be used since the FSL would cover the freesurface in place of the membrane. However, since the FSL is a thin filmstructure it can also be deposited on the membrane 112, such as incombination with radical inhibition layer.

FIG. 7 shows a top view of another embodiment of the microfluidic systemintegrated into the PμSL of the present invention. In particular, a bathvessel 200 used in a PμSL system and adapted to contain a photosensitiveresin therein is shown having multiple inlet, and outlet ports 201-206connected along its walls, and preferably near the liquid surface. Theinjection or inlet ports are indicated at 201-203, and the exhaust oroutlet ports are indicated at 204-206. Each of the inlet ports are influidic communication with one or more different types of photosensitiveresin reservoir or sources to provide the vessel basin 200′ with thedesired material. In one particular embodiment, each inlet port may beconnected with a unique material, while in an alternative embodiment,each inlet port may be connected to each of the various types of resinsavailable.

And FIG. 8 shows a combined system 300 having the features of a multipleprojection system for 3D holographic fabrication and an integratedmicrofluidic system for multiple material delivery. In particular, threeprojection systems 321-322 are shown, which project two-dimensionalimages into the fabrication zone characterized by a bath vessel 301.Similar to FIG. 36, the system includes a PμSL bath vessel 301 having acylinder 302 and a piston 303. The top of the cylinder is open andcontains a photosensitive resin. The top of the piston 303 is shown asthe fabrication stage and is connected to a z-stage 304 forlowering/elevating the fabricated part, typically in a layer-by-layerprocess. The cylinder 302 walls may be optically transparent. And ports308 and 310 are connected to the bath vessel and controlled by valves309 and 311, respectively. Furthermore a computer 305 controls thez-stage 304 and the valves 309, 311. While not shown in FIG. 8, each ofthe projections systems 301-301 may incorporate a FSL such that theimage projected into the fabrication zone is a near-field image. Andsimilar to the membrane 112 of FIG. 6, FIG. 8 also shows a membrane 312positioned at the liquid surface.

While particular embodiments and parameters have been described and/orillustrated, such are not intended to be limiting. Modifications andchanges may become apparent to those skilled in the art, and it isintended that the invention be limited only by the scope of the appendedclaims.

We claim:
 1. A holographic projection micro-stereolithography (PμSL)system, comprising: a bath containing a photosensitive resin; and atleast two light projection systems, each projection system comprising alight source; and a spatial light modulator (SLM) adapted to produce adigital image when illuminated by the light source, wherein the at leasttwo light projection systems are arranged to holographically interferesaid digital images in the photosensitive resin to volumetrically cureselect regions thereof in a holographic interference pattern.
 2. Theholographic projection micro-stereolithography (PμSL) system of claim 1,wherein each light projection system further comprises a reduction lens,and a far-field superlens (FSL) contactedly interfacing thephotosensitive resin, said FSL including a dielectric layer and a metalgrating layer, and wherein the FSL is arranged to convert a far-fieldimage produced by the SLM and reduced by the reduction lens into anear-field image for volumetrically curing the select regions of thephotosensitive resin.
 3. A holographically-controlled volumetric curingmethod of photosensitive resin, comprising: providing a bath containinga photosensitive resin, and at least two light projection systems, eachlight projection system comprising a light source and a spatial lightmodulator (SLM) adapted to produce a corresponding digital image whenilluminated by the light source; activating the light projection systemsto produce the digital images; and directing the digital images of thelight projection systems to holographically interfere in thephotosensitive resin so as to volumetrically cure select regions thereofin a holographic interference pattern.
 4. The method of claim 3, whereineach light projection system further comprises a reduction lens, and afar-field superlens (FSL) contactedly interfacing the photosensitiveresin, said FSL including a dielectric layer and a metal grating layer,and wherein the FSL is arranged to convert a far-field image produced bythe SLM and reduced by the reduction lens into a near-field image forvolumetrically curing the select regions of the photosensitive resin.